1. Field of the Invention
The invention relates to a feed pump for arrangement in a baffle of a motor vehicle fuel tank, the feed pump having a driven impeller rotatably arranged in a pump casing with a plurality of rings or guide blades delimiting blade chambers, the rings concentrically surrounding one another, and part-annular channels arranged in the pump casing opposite the rings of blade chambers and extending from an inlet channel to an outlet channel.
2. Description of the Related Art
Feed pumps produced in the form of peripheral or side-channel pumps are known from practice. The known feed pumps may be of multistage design. For example, the feed pump may be designed for feeding fuel from a fuel tank to a baffle and simultaneously feeding fuel from the baffle to an internal combustion engine of the motor vehicle. The impeller of the known feed pump is typically fastened on a shaft of an electric motor. Part annular chambers are arranged in a pump casing of the feed pump corresponding to rings of guide blades which delimit blade chambers in the impeller. Between the part-annular channels, the pump casing is located with particularly slight clearance opposite the impeller to form a sealing gap. This configuration allows a plurality of pumping stages to be arranged on a single impeller. Each of the pumping stages may be designed freely for the respective application.
A problem of the known feed pump is that a pressure difference between the part-annular channels one surrounding the other leads to an overflow of the fed liquid and consequently to high axial forces on the impeller. The overflow therefore reduces the efficiency of the feed pump.
It is an object of the present invention to provide a feed pump having part-annular channels one surrounding the other and corresponding to rings of guide blades on an impeller such that liquid to be fed is prevented from flowing between the part-annular channels.
The object of the present invention is met by a feed pump with an impeller having an end face with a plurality of levels in the axial direction of the driven shaft on which the impeller is mounted so that at least two rings of guide blades are arranged at two different levels along the axial direction.
This configuration allows the sealing gap to be made particularly long thereby providing particularly high resistance to an overflow of the liquid to be fed. In comparison with the known feed pump with a sealing gap having the same width, the feed pump according to the present invention allows only a particularly small amount of liquid to flow from one part-annular channel to another part-annular channel. Axial forces acting on the impeller are thereby kept particularly low. The feed pump according to the present invention consequently has a particularly high efficiency. Another advantage of this configuration is that the two levels arranged in the impeller require that the impeller to be inserted in the casing in the correct position. This ensures that impeller is rotated in the intended direction of rotation by the shaft of the electric motor.
According to an embodiment of the present invention, the sealing gap may be kept particularly small if an axial play of the impeller is provided. Furthermore, the impeller may have a continuous collar for separating the different levels and the pump casing may have a step corresponding to the collar.
According to another embodiment of the present invention, the impeller and the pump casing may be manufactured particularly cost-effectively when the collar is designed cylindrically.
The feed pump requires a particularly small axial construction space when the inlet channel or the outlet channel of the radially inner part-annular channel is led radially outward through a web in the pump casing arranged between the outlet channel and the inlet channel of the radially outer part-annular channel.
A radially inner ring of guide blades is arranged on a first level and a radially outer ring of guide blades is arranged on a second level, wherein a plane of the first level at a greater distance from an electric motor driving the impeller than the plane of the second level. This configuration contributes facilitates further reducing the axial dimensions of the feed pump. When the feed pump is mounted with the electric motor, the radially outer part-annular channel may be arranged at least partially radially outside the electric motor. When the feed pump is mounted in the baffle of a fuel tank, the radially inner ring of blade chambers may thereby be arranged at a particularly low level thereby avoiding a high suction head. A high suction head leads to the formation of gas bubbles and therefore to a sharp drop in the efficiency of the feed pump, particularly where the medium to be fed is hot fuel. Locating the radially inner ring of blade chambers at a particularly low level facilitates a high efficiency in the feed pump according to the present invention.
According to another embodiment of the invention, the blade chambers of the radially inner ring of guide blades have large diameter and are designed for feeding as large a volume flow as possible. In this embodiment, the impeller is thicker in the region of the radially inner ring of guide blades than in the region of the radially outer ring of guide blades.
A feed pump having high feed pressure provided when fuel is intended to be fed to the internal combustion engine of a motor vehicle and with as large a volume flow as possible to be fed into the baffle may be designed with a particularly simple design when the blade chambers of the radially inner ring of guide blades have approximately double the diameter of the blade chambers of the radially outer ring of guide blades.
According to another embodiment of the present invention, an axial feed of the fuel through the feed pump may be achieved at particularly low outlay in terms of construction when the impeller has in the radially outer region of its end faces rings of guide blades located opposite one another for forming blade chambers therebetween, wherein the blade chambers on opposite sides of the impeller are connected to one another.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.